Magnetic resonance imaging apparatus and magnetic resonance imaging method

ABSTRACT

A magnetic resonance imaging apparatus includes control means  107  and  108  for continuously performing magnetic resonance imaging of a cross section including a portion subjected to measurement of an examinee ( 10 1) at a predetermined time interval, operation means  108  for calculating diagnosis information related to the portion subjected to measurement by using a plurality of sets of nuclear magnetic resonance signals related to cross sections imaged at different time points by measuring nuclear magnetic resonance signals generated from the examinee  101 , and a position detection device  118  having a detection camera  118   b  for detecting in non-contact manner the position (three-dimensional position and rotation angle around an orthogonal coordinate axis) of a pointer  118   a  provided outside the examines body and moving while interlocked with the biological movement of the examinee  101 . The control means  108  sets the position of the cross section according to the position of the pointer  118   a  detected by the position detection device  118 , thereby eliminating an affect of the biological movement and improving the accuracy and the reliability of the diagnosis information including differential processing of a portion subjected to measurement.

TECHNICAL FIELD

The present invention relates to a magnetic resonance imaging(hereinafter, referred to as MRI) apparatus and a magnetic resonanceimaging method. Specifically, the present invention relates to setting aslice of the magnetic resonance imaging that is suitable for performingthe continuously imaging of a portion subjected to measurement of anexaminee which is moved by biological movement such as breath movement.

BACKGROUND ART

An MRI apparatus excites particular atomic nuclei (for example, protons)constituting an examinee by applying radio-frequency magnetic fieldpulse (hereinafter, referred to as an RF pulse) together with a gradientmagnetic field for setting the slice to the examinee placed In a staticmagnetic field. The MRI apparatus reconstructs a tomogram inside theexaminee based on a nuclear magnetic resonance (NMR) signals generatedby the excitation to provide the tomogram with the diagnosis The MRIapparatus is used to set a slice including an object portion ofdiagnosis, to continuously obtain tomograms of the slice in a timeseries, for obtaining various types of information necessary fordiagnosis based on the tomograms obtained at different time points.

For example, in recent years, attention is paid to an interventional MRIapparatus (hereinafter, referred to as an IVMR apparatus) in which theMRI apparatus is used for monitoring during an operation. Treatmentsusing the IVMR are, for example, a laser treatment, coagulation bymicrowave, injection of medicine such as ethanol, RF irradiatingresection, and a low temperature treatment. In these treatments, the MRIapparatus plays role as a real time imaging guide for causing ainserting needle and a thin tube to reach an affected part, a monitorfor visualizing a change of a tissue being treated, a temperaturemonitor of a portion subjected to a heating or cooling treatment, andthe like. As an example of a typical application of the IVMR, it ismentioned to obtain an image of temperature distribution of a treatedportion of the like of an examinee during a laser irradiation treatmentand microwave coagulation.

The method of obtaining the image of temperature distribution describedabove includes a method of obtaining the signal intensity, a method ofobtaining from a diffusion coefficient, a method of obtaining from thephase shift of protons (PPS. i.e. proton phase shift method), and thelike. That is, the temperature is measured in use of the property thatsignal intensity from a tissue is changed in response to the temperatureor the property that a diffusion coefficient of the Brownian movement ofwater and the like constituting a tissue is affected by temperature,wherein the PPS method demonstrates the best measuring accuracy.

In the FPS method, the temperature distribution is determined from thephase information of echo signals obtained by, for example, inversion ofgradient magnetic field. Specifically, a phase distribution isdetermined from the real part Sr and the imaginary part Si of a compleximage obtained by subjecting the echo signals to Fourier transformationusing the following equation (1).φ(x, y, z)=tan³¹ ¹(Si(x, y, z)/Sr(x, y, z))   (1)

Then, the temperature T in the following equation (2) is determined fromthus obtained phase distribution, an interval (echo time) TE between atiming of the maximum echo signal and a 90° pulse, a resonance frequencyf, and a water temperature coefficient.T[° C.]=φ[°]/{TE[s]*f[Hz]*0.01[ppm/° C.]*10⁻⁶*360[°]}  (2)

A distribution of temperature change of the examinee at a certain timecan be obtained by determining the difference between the temperaturedistributions calculated from the signals obtained at different timepoints t1 to tn (n is the number of imaging time points) using the abovemethod.

As described above, when the temperature is monitored by MRI, the sametemperature change region (a region subjected to measurement) must beconstantly in order to obtain continuous time series data, to determinethe difference between the spatial phase distributions obtained atdifferent time points, and to determine a temperature change. However,when an imaging cross section is fixed in a space, the region subjectedto measurement is often out of the imaging cross section movement of theexaminee, in particular, in the abdomen, by an affect of breathmovement. Therefore, it is difficult to stably image the regionsubjected to measurement. For example, the thickness of the imagingcross section(slice) is in the order of several millimeters to tenmillimeters, whereas the breath movement is in the range of 10 mm ormore in an interval of about three seconds. Thus, it may occur that atomogram measured at a time phase includes the region subjected tomeasurement, and a tomogram measured at another time phase does notinclude the region. Accordingly, in case of a heat treatment, themeasured time series date includes both data having information oftemperature increase in a heated portion and data without theinformation of temperature increase. In the latter case, the informationof temperature increase caused by heating cannot be obtained. To copewith the above problem, when it is intended to measure and display atemperature change in real time using a difference between the timeseries data. The temperature sometimes increases and sometimes does notincrease, or in some cases a heating region suddenly expands ordisappears, whereby the temperature cannot be stably monitored.Therefore, the result lacks reliability.

The above problem in measurement caused by movement of an examinee is acommon problem when diagnosis is executed by measuring continuously andin time series the NMR signals from an imaging cross section including aregion subjected to measurement and comparing the measured data of aplurality of imaging cross section obtained at different times, inaddition to the measurement of the temperature distribution describedabove. For example, MR angiography known as a blood vessel imagingmethod includes an image processing to improve the contrast of aparticular portion such as a blood vessel by determining the differencebetween two blood vessel images obtained at offset times. In this case,when the positions of blood vessel in the two images are displaced bymovement, there is a problem such that a blood vessel Is blurred. In aconventional teaching, in such a case, the positional displacement ofthe two images is corrected by determining the amount of positionaldisplacement based on the feature of the positional displacement thatappears in a differential image (refer to JP2001-252262A). However,since the correction is executed after obtaining the images, it cannotbe applied to a case where real time processing is required. Further, asanother example of the MR angiography, blood flow information ismeasured and drawn by taking an image of a plurality of blood vesselcross sections while moving a slicing plane in parallel along theextending direction of a blood vessel (refer to JP2002-253527A). Inthis-case, when the positions of blood vessel in images are displaced bybody movement, a measurement error arises. That is, when a portionsubjected to measurement is located outside a field of view, the portioncannot be used for comparison, or when the positions of the portionssubjected to measurement in the images are relatively displaced,differential image includes an error.

Accordingly, a first object of the present Invention is to enablepositioning of an imaging cross section in conformity with movement of aportion subjected to measurement caused by body movement when theportion subjected to measurement is continuously taken as image.

Further, a second object of the present invention is to improve accuracyand reliability of temperature monitoring by avoiding an affect of bodymovement when the distribution of temperature changes of a particularportion such as a treatment portion is measured.

DISCLOSURE OF THE INVENTION

To achieve the first object, there is provided a magnetic resonanceimaging method of the present invention comprising the steps of : takingtime series images of a measuring cross section including a portionsubjected to measurement of an examines using a magnetic resonanceimaging, and obtaining diagnosis information by comparing magneticresonance signals related to the plurality of the measuring crosssections obtained above in an operation process, wherein a body movementof the examinee is detected and a position of the movement of theexaminee is detected and a position of the measuring cross section isset so as to include the portion subjected to measurement in conformitywith the detected body movement.

A magnetic resonance imaging apparatus of the present invention forembodying the imaging method includes a means for generating a uniformstatic magnetic field in a space where an examinee is placed, a meansfor generating a gradient magnetic field for determining an image-takingcross section of the examines, a means for applying a radio-frequencymagnetic field to the space, a means for detecting nuclear magneticresonance signals generated from the examinee, a control means forcontinuously executing magnetic resonance imaging of the image-takingcross section including the portion subjected to measurement of theexaminee at time intervals, a means for operating the diagnosisinformation of the portion subjected to using a plural sets of nuclearmagnetic resonance signals of the image-taking cross section detected bythe detection means and executed at different time points, and a meansfor displaying the diagnosis information, further including a bodymovement detection means for detecting a body movement of the examinee,and the control means sets the position of the image-taking crosssection based on the information from the body movement detection means.

In this case, the control means can determine the position of theportion subjected to measurement based on the information from the bodymovement detection means and set the position of the above determinedportion subjected to measurement.

First, the body surface or a body surface portion (hereinafter, simplyreferred to as the body surface and the like) of the examinee is movedin correlation to the body movement of the examinee moved by his breathand the like. Further, a certain correlation exists between a movementof the body surface and the like and a movement of the portion subjectedto measurement in the examinee. Accordingly, it is possible to detectthe position of a pointer moving in association with, for example, thebody surface and the like in real time and to detect the movement of theportion subjected to measurement by calculation executed based on theabove correlation. The movement of the portion subjected to measurementis expressed by a change of a three-dimensional position or by a changeof a three-dimensional position and a rotation angle about orthogonalcoordinate axes (hereinafter, referred to as a six-dimensionalposition). Then, the position of the image-taking cross section is setso that the portion subjected to measurement is located at the sameposition by moving the image-taking cross section in parallel or alongthe image-taking cross section in conformity with the three-dimensionalposition of the portion subjected to measurement having been detected.As known well, the setting is conducted by adjusting the gradientmagnetic fields in the direction of three orthogonal axes. Further, whenthe six-dimensional position is detected, the gradient angle of theimage-taking cross section is set with respect to, for example, a bodyaxis, in addition to the setting of the three-dimensional position ofthe image-taking cross section.

As described by setting the position of the image-taking cross-sectionin the magnetic resonance imaging continuously executed with timeintervals in real time in conformity with the movement of the portionsubjected to measurement, it is possible to eliminate an error in theoperation process for obtaining necessary diagnosis information bycomparing the nuclear magnetic resonance signals related to theplurality of image-taking cross sections obtained at different timepoints.

To achieve the second object, the operation means is characterized byhaving a function for determining the temperature or the temperaturedistribution of the portion subjected to measurement based on thenuclear magnetic resonance signals, determining the temperature or thetemperature distribution difference of the same portion subjected tomeasurement according to the slices at different times, and determiningthe temperature change or the temperature change distribution of theportion subjected to measurement.

With the above function, it is possible to improve the accuracy and thereliability in temperature measurement. Further, the temperature changeof the portion subjected to measurement can be monitored by displayingthe thus-determined temperature change distribution as a color image.

Further, as another example of the operation means for determining thenecessary diagnosis information, there are an operation process forreconstructing an MR image of a blood vessel image and the like of aportion subjected to measurement based on nuclear magnetic resonancesignals and creating a differential image of the MR images of the bloodvessel image and the like of the same portion subjected to measurementat different time points, and the like. In this case, it is possible toimprove image quality by refining the blur of the blood vessel image andthe like.

Next, examples of the biological movement detection means for detectingthe biological movement will be specifically explained.

(1) A position detection means is arranged by disposing a pointer on thebody surface of the examinee or in relation to the body surface anddisposing a plurality of detectors at positions apart from the pointer.Then, signals are transmitted and received between the plurality ofdetectors and the pointer through a space, and the position of thepointer is detected based on the positional relation between theplurality of detectors and the pointer. A known position detectiondevice can be used as the position detection means, and when theposition detection means is classified in principle, there can beapplied a position detection means employing a system that detects theposition of the pointer by transmitting and receiving light signals,ultrasonic wave signals, electromagnetic wave signals, and the likebetween the detectors and the pointer.

(2) As a position detection means using light, there is a positiondetection means that uses, as the pointer, a reflector for reflectinglight and has a light emitter and two cameras disposed apart from thepointer and detects the three-dimensional position of the pointer basedon the two images formed by receiving the light of the light emitter,which is reflected by the reflector, by the two cameras.

(3) As another example of the position detection means using light,there is a position detection means that uses, as the pointer, threereflectors for reflecting light disposed at the apexes of a triangle andhas a light emitter and two cameras disposed apart from the pointer anddetects the three-dimensional position and the rotation angle about anorthogonal coordinate axis of the pointer based on the two images formedby receiving the light of the light emitter, which is reflected by thereflectors, by the two cameras. As an example of the position detectionsystem, there Is known POLARIS (commodity name) of Northern DigitalInstrument.

Further, the pointer is fixed in contact with a body surface near to aportion subjected to measurement or fixed to a needle device insertedinto an examinee at a position outside of the examinee (for example, therear end of the needle device). When the three reflectors are disposeddiscretely, it is preferable to dispose them at the apexes of atriangle. The needle device is composed of a laser fiber passed througha guide inserted into a treatment portion for warming it, an electrodeinserted into a treatment portion for irradiating micro waves thereto,and the like. When any of these needle devices is used, the temperatureof the needle device is measured at the extreme end thereof. In thiscase, although the needle device may be turned about its axis, it is notnecessary to turn a slice in accordance with the turn of the needledevice. Thus, it is preferable to execute such a correction as toextract the rotation angle component about the axis of the needle devicefrom the rotation angle about an orthogonal coordinate axis of thepointer detected by the position detection means and to subtract therotation angle component about the axis of the needle device from therotation angle about an orthogonal coordinate axis of the pointer.

Further, it is preferable to previously determine the correlation databetween the movement of the portion subjected to measurement caused bybiological movement and the movement of the pointer and to determine thethree-dimensional position and the rotation angles about the orthogonalcoordinate axes of the portion subjected to measurement from thethree-dimensional position and the rotation angles about the orthogonalcoordinate axes detected by the position detection means based on thecorrelation data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the overall arrangement of an MRI apparatus towhich the present invention is applied.

FIG. 2 is a view showing an important portion of a position detectiondevice.

FIG. 3 is a flowchart showing an embodiment related to a temperaturemeasuring procedure by the MRI apparatus according to the presentinvention.

FIG. 4 is a view showing an example of a pulse sequence employed intemperature measurement.

FIGS. 5(a) to 5(d) are views explaining temperature measurementaccording to the present invention.

FIG. 6 is a graph schematically showing a change of a temperature changeregion due to body movement.

FIG. 7 is a view showing another embodiment of the temperaturemeasurement according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of an MRI apparatus of the present invention will bedescribed below with reference to the drawings. FIG. 1 is a view showingthe overall arrangement of the MRI apparatus to which the presentinvention is applied. The MRI apparatus includes a static magnetic fieldgeneration magnetic circuit 102 composed of an electromagnet or apermanent magnet for generating a uniform static magnetic field H0 in anexaminee 101, a gradient magnetic field generation system 103 forgenerating gradient magnetic fields Gx, Gy, Gz the intensities of whichlinearly change in three axis directions which are orthogonal to eachother, a transmission system 104 for applying a radio-frequency magneticfiled (RF pulses) to the examinee 101, a detection system 105 fordetecting NMR signals generated from the examinee 101, a gradientmagnetic field generation system 103, a sequencer 107 for transmitting acommand to the transmission system 104 and the detection system 105 andgenerating gradient magnetic fields and the RF pulses at a predeterminedtiming, a computer 108 for executing various processings such as thecontrol of the sequencer 107, image processing, and temperaturecalculation, a signal processing system 106 for displaying and storingan image, an operation unit 121 including a keyboard 112 and a mouse 123for executing operations for setting various parameters such as imagingconditions to the computer 108, and a position detection device 118including pointers 118 a and a detection camera 118 b for detecting theposition of a particular portion of the examinee 101 lying on a bed.

The gradient magnetic field generation system 303 includes gradientmagnetic field coils 109 a and 109 b in the three axis directions and apower supply 110 thereof, determines a slice of the examinee 101depending on a manner of applying gradient magnetic fields, and providesthe NMR signals generated by the examinee 101 with position information.In the present invention, the gradient magnetic fields for determiningthe slice are controlled based on the position information from theposition detection device 118 through the computer 108.

The transmission system 104 includes a synthesizer 111, a modulator 112,a power amplifier 113, and a transmission coil 114 a, modifies theradio-frequency generated by the synthesizer 111 through the modulator112 at the timing commanded by the sequencer 107, amplifies the thusmodified radio-frequency through the power amplifier 113, and suppliesit to a transmission coil 114 a. In the above operation, aradio-frequency magnetic field is generated in the examinee 101, andnuclear spin is exited.

The detection system 105 includes composed of a detection coil 114 b, anamplifier 115, an orthogonal phase detector 116, and an A/D converter117, receives the NMR signals generated from the examinee 101 by thedetection coil 114 b, amplifies the NMR signals by the amplifier 115,detects the signals by the orthogonal phase detector 116 with referenceto the reference radio-frequency signals from the synthesizer 111, andinputs NMR signals to the computer 108 as a two sets of digital signals.

Although the transmission coil 114 a and the detection coil 114 b areseparately provided in the figure, it is also possible to use a singlecoil having both a transmission function and a reception function.

After the computer 108 subjects the signals input from the detectionsystem 105 to predetermined signal processing, it calculates a nuclearspin density distribution, a relaxation time distribution, a spectrumdistribution, a temperature distribution, and the like and creates animage. Further, in the present invention, the computer,108 captures thesignals as to the position information of a portion subjected tomeasurement of the examinee from the position detection device 118,determines the position of a slice based on the position information,and outputs a command for generating gradient magnetic fieldscorresponding to the slice to the sequencer 107.

The image formed by the computer 108 is displayed on a display 128 ofthe signal processing system 106 and stored in a magnetic disc 126, anoptical magnetic disc 127, and the like when necessary. Meanwhile, thesignal processing system 106 has a ROM 124 and a RAM 125 storing data incourse of calculation, various parameters necessary for calculation, andthe like.

The position detection device 118 detects a particular region of theexaminee 101, specifically, a position (coordinate) in the measurementspace of an object region where a temperature change is measured.Signals as to the information of a position detected by the positiondetection device 118 are transmitted to the computer 108 through a line.The computer 108 determines the position of the slice of the examinee101 based on the signals as to the information of the detected position.As shown in FIG. 2, for example, the position detection device 118includes pointers 118 a (three sets in the illustrated example) fixed onthe body surface of the examinee 101 in the vicinity of an objectmeasuring region 201 and a detection camera 118 b having two cameras fordetecting the positions of the pointers 118 a in order to indicate thespecific region of the examinee 101. A known pointer developed to obtainan MR image as to a desired position can be used as the pointer 118 a.Specifically, an active- or passive-type pointer having at least threeinfrared ray emitting diodes or reflection bulbs disposed at the apexesof a triangle can be used. The passive-type diodes are preferable inoperability because they do not need a power supply line. The detectioncamera 118 b is composed of at least two cameras attached at positionshaving a parallax with respect to the pointers, and when thepassive-type pointers using the reflection bulbs are used, the camerasare provided with light emitting diodes acting as light emitters forilluminating the reflection bulbs. The detection camera 118 b isdisposed at a position, i.e. 1 m to 1.5 m apart from the center of thestatic magnetic field generating region of the MRI apparatus.

The pointers 118 a can be disposed at a predetermined portion such as atreatment portion and the rear end (portion remaining outside of theexaminee's body) of an instrument (for example, an Inserting needle andan inserting guide) that is inserted into the examinee 101, other thanon the body surface of the examinee 101. Then, the two cameras detectthe positions of the respective light emitting diodes or the reflectionbulbs of the pointers 118 a in real time and send the six-dimensionalposition information of the center points of the pointers 118 a (thatis, rotational information as to x-, y-, and z-axes) to the computer 108in real time. A position detection device POLARIS of Northern DigitalInstrument, for example, can be used as the position detection device118 arranged as described above, and a detection speed of 20 to 60 MHzand a position accuracy of 0.35 mm can be realized by the positiondetection device. Meanwhile, when only the three-dimensional position ofthe pointer 118 a is detected, the pointer 118 a can be formed of onelight emitting diode or one reflection bulb.

Meanwhile, although not illustrated, a reference pointer is disposed ata fixed position apart a predetermined distance from the center of amagnetic field to convert the positions of the pointers 118 a into acoordinate from the center of the magnetic field in the measurementspace of the MRI apparatus. That is, as an initial operation, theposition of the reference pointer is detected by the detection camera118 b, the position of the reference pointer, for example, is determinedas the point of origin of a measurement space coordinate, and thecoordinates of the positions of the pointers 118 a in the measurementspace coordinate are detected.

Next, a temperature measuring method executed using the MRI apparatuswill be explained with reference to FIGS. 3 to 5. The temperaturemeasurement using the MRI apparatus is applied when treatments such as alaser treatment, coagulation by microwave, injection of medicine such asethanol, RF irradiating resection, and a low temperature treatment areexecuted, and when a simple operation is executed by IV-MR in order tomonitor the local temperature of an object portion during the treatmentsor the operation.

First, as shown in FIG. 2, the pointers 118 a of the position detectiondevice 118 are disposed in the vicinity of the object temperature changeregion 201 on the body surface of the examinee 101 placed in themeasurement space and the detection camera 118 b starts to measure thepositions of the pointers 118 a in real time. Next, the detection camera118 b starts to photograph a cross sectional surface S1 including thetemperature change region 201. The cross sectional surface S1 that isimaged first is determined by imaging and displaying an image along, forexample, the body axis direction of the examinee and selecting a crosssectional surface including an object portion from the image, similar toa case that an ordinary image is taken. A gradient magnetic fieldcorresponding to the cross sectional surface S1 selected as describedabove is determined, and the thus determined gradient magnetic field isset as a parameter of a slice.

Image-taking is executed by the pulse sequence of a gradient echo method(GRE) as shown in, for example, FIG. 4. That is, a gradient magneticfield Gs 402 for selecting the slice is applied together withradio-frequency magnetic field pulses (RF pulses) 401, then a phaseencode gradient magnetic field Gp 403 is applied, and a gradient echoSig. 405 is measured while applying a read-out gradient magnetic fieldGr 404 having an inverting polarities. The sequence is executedrepeatedly while changing the intensity of the phase encode gradientmagnetic field Gp 403 and measuring a set of the signals includingtemperature information of the slice. A phase distribution φ1(x, y, z)is determined from the real part and the imaginary part of complex imagedata, which is obtained by subjecting the echo signals to Fouriertransform, using the above equation (1).

As shown in FIG. 5(b), the image of the thus obtained phase distributionreflects the temperature information of the slice S1 including thetemperature change region 201. A time at which the image of the phasedistribution Is set to t1, the same measurement is executed at a time t2after Δt passes from the time t1. However, in this case, the position ofthe temperature change region 201 changes from a position P1 at the timet1 to P2 by breath movement as shown in FIG. 5(a). The computer 108captures the six-dimensional position information of the pointers 118 afrom the position detection device 118 (step 301 of FIG. 3), calculatesthe slice S2 Including P2 by calculating the six-dimensional position ofP2 and determines a gradient magnetic field Gs 402 for selecting theslice S2 (step 302). Then, a command is sent to the sequencer 107 sothat the newly determined gradient magnetic field is used as thegradient magnetic field for selecting the slice when the pulse sequencerof FIG. 4 is executed. Then, at the time t2, the newly selected theslice S2 is measured (step 303).

Although the phase distributions φ1 and φ2 obtained at the times t1 andt2 described above select the different slices in the measurement space,they act as the phase distribution of approximately the same sliceincluding the same temperature change region in the examinee being moved(FIG. 5(c)). The complex difference between these two phasedistributions φ1 and φ2 is calculated, and a temperature changedistribution ΔT is calculated based on the temperature difference(T1−T2) between the times t1 and t2 by an equation (3) (step 304).ΔT−T 1−T 2=(φ1−φ2)/TE*f*0.01*10⁻⁶*360)   (3)

The image of the thus obtained temperature change distribution (FIG.5(d) is displayed on the display (step 305). Thereafter, the slicecorresponding to the positions of the pointers is imaged at everypredetermined time interval, and temperature change distributions aredetermined from a phase distribution φ1 calculated as to the slice andthe phase distribution φ1 determined first and sequentially displayed onthe display. An operator can execute a treatment such as warming whilemonitoring the image of the temperature change distribution displayed onthe display.

Although the temperature change distribution is determined from thecomplex difference between the i-th phase distribution φ1 and the phasedistribution φ1 determined first at step 304, a temperature changedistribution Ti from the beginning of measurement may be determined bycalculating a temperature change distribution ti by determining thecomplex difference between the i-th phase distribution φ1 and an(i+1)-th phase distribution φ (i+1) and cumulating the temperaturechange distribution ti (Ti−Σti). That is, a phase change of (φ1−φ1)>360°may occur, this method is effective when there is a large phase change.

Further, the example FIG. 5(a) shows a case that the temperature changeregion 201 simply moves up and down as shown by an arrow, that is, acase that the slices S1 and S2 move in parallel with each other.However, the embodiment is not limited thereto, and even if the positionof the temperature change region 201 moves six-dimensionally, thegradient magnetic fields Gs 402, Gp 403, and Gr 404 can be set bydetermining the six-dimensional position (the three-dimensional positionand the rotation angle about orthogonal coordinate axes) of the slice S2based on the position information by which the six-dimensional positionsof the pointers 118 a are detected.

As described above, according to the embodiment, since a phasedistribution image including the same temperature region can be obtainedat all times even a slice is different in the space, the temperaturechange of the temperature change region whose temperature is measuredcan be securely monitored, thereby the accuracy of a warming treatmentand the like can be improved. Furthers the temperature change of theportion subjected to measurement can be monitored by displaying thedetermined temperature change distribution as a color image.

Further, in the embodiment described above, the positions at which thepointers 118 a are disposed and which are detected by the positiondetection device 118 are not the same as the position of the temperaturechange region 201. However, in the region, in which it can be regardedthat the temperature change region is interlocked with the movement ofthe pointers 118 a, the position of a slice can be calculated byregarding the movement of the pointers 118 aas the movement of thetemperature change region as it is.

Meanwhile, when the variation 601 of the temperature change region isinterlocked with a breath movement 602 but the amount of movement of thetemperature change region is different from that of the breath movement602 as shown in FIG. 6, a plurality of morphological images arepreviously obtained as to different time phases and the relation(displacement) between the amounts of movement is determined as shown inFIG. 6. It is possible to more accurately calculate the position of thetemperature change region by the correlation data determined previouslyand the detected center positions of the pointers 118 a. Namely, it ispreferable to previously measure the correlation data between themovement of the portion subjected to measurement caused by biologicalmovement and the movement of the pointers 118 a and to determine thethree-dimensional position and the rotation angle about an orthogonalcoordinate axis of the portion subjected to measurement from thethree-dimensional position and the rotation angles about the orthogonalcoordinate axis detected by the position detection device 118 based onthe correlation data. Further, when an internal organ acting as thetemperature change region is exposed by an incision and the like, themovement of the temperature change region can be monitored at once bydirectly disposing the pointers 118 a in the vicinity of the internalorgan.

Further, when heating is executed by a laser fiber passed through anInserted guide and when a microwave is irradiated from an insertedneedle electrode, the pointers 118 a can be disposed at the rear end ofan inserting needle 701 as shown in FIG. 7. In this method, since thepositional relation between the rear end and the front end of theinserting needle 701 is fixed, an extreme end position can be found bydetecting a rear end position. Accordingly, the slice of the temperaturechange region can be selected by directly calculating the position ofthe temperature change region at the extreme end of the inserting needle701 in the space.

Further, there are a heat device for heating a treatment portion by alaser fiber passed through an inserted guide, a device for irradiating amicrowave to a treatment portion from an inserted needle electrode, andthe like as needle devices which are used by being inserted into theexaminee as in the inserting needle 701. When these needle devices suchas the inserting needle 701 and the like are used, the extreme endsthereof act as object portions at which temperature is measured. In thiscase, the three-dimensional position and the rotation angle about anorthogonal coordinate axis of the extreme end of a needle device aredetermined based on the three-dimensional positions and the rotationangles about orthogonal coordinate axes of the pointers 118 a detectedby the position detection device 118, and the three-dimensional positionand the rotation angle about an orthogonal coordinate axis of a sliceare set such that the slice includes the axis of the needle device aswell as the three-dimensional position and the rotation angle about anorthogonal coordinate axis of the slice agree with those of the needledevice.

Further, although a needle device may be turned about its axis, it isnot necessary to turn a slice in accordance with the turn of the needledevice. Therefore, it is preferable to execute such a correction as toextract the rotation angle component about the axis of the needle devicefrom the rotation angles about orthogonal coordinate axes of thepointers 118 a detected by the position detection device 118 and tosubtract the rotation angle component about the axis of the needledevice from the rotation angles about orthogonal coordinate axes of thepointers 118 a.

According to the embodiment of the present invention for executing thetemperature measurement described above, even if a positionaldisplacement is caused by the biological movement and the like in aregion whose temperature is monitored, the temperature of the region canbe accurately measured, thereby accuracy and reliability of thetemperature measurement can be improved. The example of displaying theimage of temperature distribution is explained in the above description,and, in this case, it is also possible to numerically display atemperature, a temperature difference, and the like, in addition to theimage of temperature distribution.

Further, the present Invention is not limited to the imaging processingfor measuring the temperature change and the distribution of temperaturechanges of a portion subjected to measurement and can be also applied toan imaging method including image processing for obtaining diagnosisinformation by comparing the MR images of the same portion subjected tomeasurement measured at different times. According to the imagingmethod, since the positional dislocation of the portion subjected tomeasurement can be reduced between the images to be compared, accuracyand reliability of the diagnosis information can be improved.

An embodiment in which the present invention is applied to MRangiography of a blood vessel will be explained. The MR angiography is atechnology for drawing a blood flow image while improving the contrastof, for example, a particular portion by time series measuring the NMRsignals related to a slice including a blood vessel and subjecting aplurality of blood vessel images of the slice at different times todifferential processing, and various methods have been proposed(JP2001-252262A, JP2002-253527A). Even if any of the methods isemployed, since two blood images of the same portion at different timesare subjected to the differential processing, an error is included inthe differential processing when the blood vessel and the like are movedby biological movement. As a result, although image quality isdeteriorated by the blurring and the like of the blood vessel and thelike, the error of the differential processing can be suppressed byreducing the positional displacement of the pair of blood vessel imagessubjected to the differential processing by setting the slice inconformity with the movement of the examinee or the blood vessel.Moreover, although the conventional method of detecting and correctingthe positional displacement of the two blood vessel images is executedoff-line after they are imaged, since the slice itself can be set inconformity with biological movement in the present invention. MRangiography imaging can be executed in real time.

A procedure of an embodiment for creating the three-dimensionaldifferential image of an imaging region including an object imagingblood vessel by a method of using a contrast agent will be explained.First, before the contrast agent is injected, the region including theobject imaging blood vessel is imaged by three-dimensional MRI. At thetime, as shown in FIG. 2, the pointers 118 a are fixed on the bodysurface of an examinee, the positional changes of the pointers 118 a aredetected, and the position and the orientation of a slice are set eachtime imaging is executed based on the correlation between the previouslymeasured changes of the positions and orientations of the pointers 118 aand the changes of the position and the orientation of the blood vessel.With the above operation, even if the blood vessel is moved bybiological movement, the blood vessel is imaged at the same position andin the same orientation in an MR image. As described above,three-dimensional blood vessel images are collected before the contrastagent is injected. Next, after the contrast agent is injected, theregion including the blood vessel is imaged by known three-dimensionalMRI in exact timing with that a blood containing the contrast agentflows through an object imaging portion. At the time, the position andthe orientation of a slice are set each time imaging is executed basedon the correlation between the previously measured changes of thepositions and orientations of the pointers 118 a and the changes of theposition and the orientation of the blood vessel as in the above. Withthis operation, the blood vessels in the MR images are imaged at thesame position and in the same orientation before and after the contrastagent is injected. Accordingly, even if the blood vessel images of thesame slice are subjected to the differential processing before and afterthe contrast agent is injected, the error of a differential image can bereduced because the position of the blood vessel is displaced little oris not displaced at all. As a result, a differential image, which isless blurred and has high quality, can be obtained.

As described above, according to the embodiment, there is an advantagethat the MR angiography can be executed In real time because correctionIs made against biological movement by changing a slice in conformitywith blood movement during imaging.

It is needless to say that the present invention is by no means limitedto the MR angiography employing the method of using a contrast agent andcan be also applied to the imaging method as other MR angiography thatis disclosed in, for example, JP2002-253527A in which blood flowinformation is measured and drawn by imaging a plurality of blood vesselcross sections while moving sliced surfaces in parallel with each otheralong the direction in which a blood vessel extends.

Further, the present invention is not limited to the above embodimentand may be variously modified. For example, although FIG. 4 exemplifiesthe sequence by the gradient echo method as the pulse sequence formeasuring concentration, other sequences may be employed as long as theyare GrE sequences which can obtain echo signals in which a phasecomponent includes a temperature dependent component (resonancefrequency×static magnetic field intensity), in addition to the sequenceof FIG. 4. Specifically, known pulse sequences, for example, high speedGrE sequences such as SARGE, TRASARGE, and RFSARGE, sequences such asSSFP (Stredy State Free Precession), and the like, and GrP type EPIsequences can, be employed.

Further, although the above embodiment exemplifies the optical camera,and the optical devices such as the pointers and the like, which areimaged by the optical camera, a method of using an electromagnetic wave,and a method of using an ultrasonic wave can be appropriately used.

1. A magnetic resonance imaging apparatus comprising: means forgenerating a uniform static magnetic field in a space where an examineeis placed, means for generating a gradient magnetic field fordetermining a image-taking cross section of the examinee, means forapplying a radio-frequency magnetic field to the space, means fordetecting nuclear magnetic resonance signals generated from theexaminee, control means for continuously executing magnetic resonanceimaging of the image-taking cross section including the portionsubjected to measurement of the examinee at time intervals, means foroperating the diagnosis information of the portion subjected to using aplural sets of nuclear magnetic resonance signals of the image-takingcross section detected by the detection means and executed at differenttime points, and display means for displaying the diagnosis information,the magnetic resonance imaging apparatus, further comprising: bodymovement detection means for detecting the body movement of theexaminee, wherein the control means sets the position of theimage-taking cross section based on the information from the bodymovement detection means.
 2. A magnetic resonance imaging apparatusaccording to claim 1, wherein the control means determines the positionof the portion subjected to measurement based on the information fromthe body movement detection means and sets the position of the crosssection in conformity with the position subjected to measurement.
 3. Amagnetic resonance imaging apparatus according to claim 1 or 2, whereinthe body movement detection means comprises a pointer disposed inassociation with the examinee and a detector for detecting the signalsfrom the pointer, and the detector detects the body movement of theexaminee based on the positional relation between the detector and thepointer.
 4. A magnetic resonance imaging apparatus according to claim 1,wherein the body movement detection means includes position detectionmeans for detecting the three-dimensional position of the pointerdisposed in association with the examinee, and the control means setsthe three-dimensional position of the cross section by determining thethree-dimensional position of the portion subjected to measurement basedon the three-dimensional position of the pointer detected by theposition detection means.
 5. A magnetic resonance imaging apparatusaccording to claim 3, wherein the body movement detection means detectsthe three-dimensional position and the rotation angle about anorthogonal coordinate axis of the pointer, and the control means setsthe three-dimensional position and the rotation angle about anorthogonal coordinate axis of the cross section by determining thethree-dimensional position and the rotation angle about an orthogonalcoordinate axis of the portion subjected to measurement based on thethree-dimensional position and the rotation angle about orthogonalcoordinate axis of the pointer detected by the body movement detectionmeans.
 6. A magnetic resonance imaging apparatus according to claim 3,wherein the body movement detection means includes position detectionmeans that comprises a pointer having a reflector for reflecting lightand a light emitter and two cameras disposed apart from the pointer anddetects the three-dimensional position of the pointer based on the twoimages formed by receiving the light from the light emitter, which isreflected by the reflector, by the two cameras; and the control meanssets the three-dimensional position of the cross section by determiningthe three-dimensional position of the portion subjected to measurementbased on the three-dimensional position of the pointer detected by theposition detection means.
 7. A magnetic resonance imaging apparatusaccording to claim 3, wherein the body movement detection means includesposition detection means including a pointer having three reflectors forreflecting light disposed at the apexes of a triangle and a lightemitter and two cameras disposed apart from the pointer and detects thethree-dimensional position and the rotation angle about an orthogonalcoordinate axis of the pointer based on the two images formed byreceiving the light of the light emitter, which is reflected by thethree reflectors, by the two cameras: and the control means sets thethree-dimensional position and the rotation angle about an orthogonalcoordinate is of the cross section by determining the three-dimensionalposition and the rotation angle about the orthogonal coordinate axis ofthe portion subjected to measurement on based on the three-dimensionalposition and the rotation angle about an orthogonal coordinate axis ofthe pointer detected by the position detection means.
 8. A magneticresonance imaging apparatus according to claim 6 or 7, wherein theoperation means has correlation data created by previously measuring thecorrelation between the movement of the portion subjected to measurementmoved by body movement and the movement of the pointer and determinesthe three-dimensional position and/or the rotation angle aboutorthogonal coordinate axes of the portion subjected to measurement fromthe three-dimensional position and/or the rotation angle about anorthogonal coordinate axis detected by the position detection meansbased on the correlation data.
 9. A magnetic resonance imaging apparatusaccording to claim 1, wherein the operation means determines firstmagnetic resonance signals as a reference and second magnetic resonancesignals after body movement and determines a temperature changedistribution by calculating the difference between the temperaturedistributions of the determined sets of the portion subjected tomeasurements.
 10. A magnetic resonance imaging apparatus according toclaim 9, wherein the body movement detection means includes positiondetection means that comprises the pointer having the three reflectorsfor reflecting light disposed discretely in contact with a body surfacenear to the portion subjected to measurement and a light emitter and twocameras disposed apart from the pointer and detects thethree-dimensional position and the rotation angle about an orthogonalcoordinate axis of the pointer based on the two images formed byreceiving the light of the light emitter, which is reflected by thethree reflectors, by the two cameras; and the control means sets thethree-dimensional position and the rotation angle about an orthogonalcoordinate axis of the cross section by determining thethree-dimensional position and the rotation angle about an orthogonalcoordinate axis of the portion subjected to measurement based on thethree-dimensional position and the rotation angle about an orthogonalcoordinate axis of the pointer detected by the position detection means.11. A magnetic resonance imaging apparatus according to claim 10,wherein the operation means has correlation data created by previouslymeasuring the correlation between the movement of the portion subjectedto measurement moved by body movement and the movement of the pointerand determines the three-dimensional position and the rotation angleabout an orthogonal coordinate axis of the portion subjected tomeasurement from the three-dimensional position and the rotation angleabout an orthogonal coordinate axis detected by the position detectionmeans based on the correlation data.
 12. A magnetic resonance imagingapparatus according to claim 1 or 2, wherein the portion subjected tomeasurement is a portion including the extreme end of a needle deviceinserted in the examinee; and the operation means has a function fordetermining the temperature distribution of the portion subjected tomeasurement using the respective sets of the nuclear magnetic resonancesignals and determining a temperature change distribution by calculatingthe difference between the temperature distributions of the thusdetermined respective sets of the portion subjected to measurement. 13.A magnetic resonance imaging apparatus according to claim 13, whereinthe body movement detection means comprises position detection meansthat comprises a pointer having reflectors discretely attached to theportions of the needle device disposed outside of the body and a lightemitter and two cameras disposed apart from the pointer and detects thethree-dimensional position of the pointer based on the two images formedby receiving the light of the light emitter, which is reflected by thethree reflectors, by the two cameras; and the control means determinesthe three-dimensional positions of the extreme end of the needle devicebased on the three-dimensional position of the pointer detected by theposition detection means and sets the three-dimensional position of thecross section such that the cross section includes the axis of theneedle device as well as the three-dimensional position of the crosssection agree with that of the needle device.
 14. A magnetic resonanceimaging apparatus according to any of claims 9 to 13, wherein theoperation means includes a function for forming the temperature changedistribution of the portion subjected to measurement as an image anddisplaying the image on a display screen.
 15. A magnetic resonanceimaging apparatus according to claim 1 or 2, wherein the operation meanshas an image processing function for rearranging tomograms including theportion subjected to measurement using the respective sets of thenuclear magnetic resonance signals and determining the differentialimage of the respective sets of the rearranged tomograms.
 16. A magneticresonance imaging apparatus according to claim 1 or 2, wherein theoperation means has an image processing function for rearranging bloodvessel images including the portion subjected to measurement using therespective sets of the nuclear magnetic resonance signals anddetermining the differential image of the respective sets of therearranged blood vessel images.
 17. A magnetic resonance imagingapparatus according to claim 15 or 16, wherein the body movementdetection means includes position detection means that comprises apointer having the three reflectors for reflecting light disposeddiscretely in contact with a body surface near to the portion subjectedto measurement and a light emitter and two cameras disposed apart fromthe pointer and detects the three-dimensional position and the rotationangle about an orthogonal coordinate axis of the pointer based on thetwo Images formed by receiving the light of the light emitter, which isreflected by the three reflectors, by the two cameras; and the controlmeans sets the three-dimensional position and the rotation angle aboutan orthogonal coordinate axis of the cross section by determining thethree-dimensional position and the rotation angle about an orthogonalcoordinate axis of the portion subjected to measurement based on thethree-dimensional position and the rotation angle about an orthogonalcoordinate axis of the pointer detected by the position detection means.18. A magnetic resonance imaging apparatus according to claim 17,wherein the operation means has correlation data created by previouslydetecting the correlation between the movement of the portion subjectedto measurement moved by body movement and the movement of the pointerand determines the three-dimensional position and the rotation angleabout an orthogonal coordinate axis of the portion subjected tomeasurement from the three-dimensional position and the rotation angleabout an orthogonal coordinate axis detected by the position detectionmeans based on the correlation data.
 19. A magnetic resonance imagingmethod which comprises the steps of obtaining time series images of ameasuring cross section including a portion subjected to measurement ofan examinee using magnetic resonance imaging, and obtaining diagnosisinformation by comparing magnetic resonance signals related to theplurality of the measuring cross sections obtained in an operationprocess, wherein the body movement of the examinee is detected and aposition of the cross section is set so as to include the portionsubjected to measurement in conformity with the detected body movement.20. A magnetic resonance imaging method according to claim 19, whereinthe movement of the body surface or the movement of the portion moved inrelation to the body surface is detected by detecting thethree-dimensional position and the rotation angle about an orthogonalcoordinate axis of the body surface or the portion.